Effects of gastric loads and food deprivation on subsequent food intake in suckling rats.

Suckling rats were subjected to deprivation periods of 6-8 hr. Intake following deprivation was greater in deprived than in nondeprived sucklings, but did not increase with increasing deprivation. Gastric loads of NaCl solutions depressed subsequent intake; 3% NaCl was more effective than .9% NaCl. Other gastric loads of varying osmotic and caloric value also depressed subsequent intake. In order of increasing effectiveness in depressing intake, the gastric loads were protein hydrolystate, heavy cream, water, milk, lactose, glucose, and corn oil. Effectiveness was unrelated to osmotic or caloric value of the load. Gastric fill and, possibly, some property of carbohydrate appear to be important determinants of satiety in the suckling rat.     

The rate and amount of food intake as determinants of vomiting

Vomiting of nonmedical origin by retarded persons has been found to be greatly influenced by reinforcement procedures. To explicate the possible influence of the rate and amount of food intake, a satiation procedure and a spaced-eating procedure were provided to three profoundly retarded adults with this problem. Vomiting was found to double or triple after satiation for each subject, and to decrease during spaced eating for each subject; the decrease was especially great for the two subjects who learned to eat most slowly after extended spaced eating training. These results suggest that vomiting is caused in large part by excessive stomach loading and can be effectively treated by reducing the eating rate and/or amount of food intake. This generalization may also apply to infants and to the bulimic binge-purge cycle of nonretarded adults.     

Effects of anorectic drugs on food intake under progressive-ratio and free-access conditions in rats

The effects of two anorectic drugs, dexfenfluramine and phentermine, on food intake under different food-access conditions were examined. Experiment 1 compared the effects of these drugs on food intake under a progressive-ratio (PR) schedule and free-access conditions. Dexfenfluramine decreased food intake under both conditions, but the doses required to decrease intake under free-access conditions were higher than those required to reduce intake under the PR condition. Intermediate doses of phentermine sometimes increased breaking points, and higher doses decreased them. Phentermine decreased food intake at the same doses under both access conditions. Thus the potency of dexfenfluramine, but not phentermine, to decrease food-maintained behavior depended upon the food-access condition. Experiment 2 used a novel mixed progressive-ratio schedule of food delivery to study the duration of drug effects. Sessions consisted of five components separated by 3-hr timeouts. The ratio requirement reset at the beginning of each component and a new breaking point was obtained. Both dexfenfluramine and phentermine dose-dependently decreased breaking points early in the session. In some rats, compensatory increases in breaking point were observed. That is, breaking points later in the session increased over control levels, resulting in no change in the total number of food pellets earned for the session compared to control. The present findings suggest that the effects of some anorectic drugs depend upon the access conditions for food; increasing the effort to obtain food may enhance their ability to decrease food-maintained behavior.     

Nest material and food as reinforcers for fixed-ratio responding in mice

Three experiments investigated the importance of operant-reinforcer distance as a factor affecting continuous reinforcement (CRF) and fixed-ratio (FR) performance in mice, with nest material and food as reinforcers. In Experiment 1, nest material (paper strips) was presented on a series of FR schedules of increasing size, with the operandum located as close as possible to the reinforcer dispenser. Subjects compensated for increases in FR size by proportionately increasing their response output, but ratio strain occurred at low FR values. In Experiment 2, response rate was found to be inversely related to operant-reinforcer distance on a CRF schedule with nest material as reinforcer. In Experiment 3, food was presented on a series of FR schedules at two levels of deprivation, and with three operant-reinforcer distances. Operant-reinforcer distance was found to affect CRF response rate, degree of compensation for increases in FR size, and occurrence of ratio strain, but only when deprivation level was low. The results support the view that nest material and food share fundamentally similar reinforcing properties, but that nest material is a weaker reinforcer under normal test conditions.     

Reactions to daily events as a function of familiarity with an environment

Undergraduate participants provided measures of their psychological well‐being and described the positive and negative events that occurred each day, once during the first and second semesters of an academic year. For four of the five measures of daily well‐being, reactivity to negative events decreased from the first to second semester, whereas for four of the five measures of well‐being, reactivity to positive events did not change over the year. These results suggest that familiarity with an environment moderates reactivity to negative daily events. As people become more familiar with an environment, negative events may elicit smaller decreases in well‐being. In contrast, increases in well‐being elicited by positive events appear to be unrelated to familiarity with the environment. More broadly, these differences suggest that the reactivity to positive and negative events reflect the operation of different processes. Copyright © 2007 John Wiley & Sons, Ltd.